The -Dsrv PRGRS_MAX_BLOCKSIZE,nnn option where nnn is the size in bytes, indicates the total allowable memory available to all cursors established as block cursors. This value limits the total memory available to all block cursors irrespective of the table to which it is allocated. ODBC_DEF_MAXBLOCKSZ sets the default size which is currently 1MB. The overall memory allocated to block cursors by the DataServer connection cannot exceed the value set for PRGRS_MAX_BLOCKSIZE. Any block cursor that will place memory consumption over this threshold will be rejected as a block cursor and instead be established as a lookahead cursor.